The following relates to counterfeit prevention. It finds particular application in utilizing miniature security marks to distinguish authentic documents and/or images from counterfeit documents and/or images.
Current counterfeit prevention systems are mainly based on the use of digital watermarks. Digital watermarking is a technique which allows a user to add information (e.g., copyright notices, security codes, identification data, etc.) to digital image signals and documents. Such data can be in a group of bits describing information pertaining to the signal or to the author of the signal (e.g., name, place, etc.).
Most common watermarking methods for images work in spatial or frequency domains. There are various spatial and frequency domain techniques used for adding watermarks to and removing them from signals.
For spatial digital watermarking the simplest method involves flipping the lowest-order bit of chosen pixels in a gray scale or color image. This will work well only if the image will not be subject to any human or noisy modification. A more robust watermark can be embedded in an image in the same way that a watermark is added to paper. Such techniques may superimpose a watermark symbol over an area of the picture and then add some fixed intensity value for the watermark to the varied pixel values of the image. The resulting watermark may be visible or invisible depending upon the value (large or small, respectively) of the watermark intensity.
Spatial watermarking can also be applied using color separation. In this way, the watermark appears in only one of the color bands. This renders the watermark visibly subtle such that it is difficult to detect under regular viewing. However, the watermark appears immediately when the colors are separated for printing or xerography. This renders the document useless to the printer unless the watermark can be removed from the color band. This approach is used commercially for journalists to inspect digital pictures from a photo-stockhouse before buying un-watermarked versions.
There are several drawbacks to utilizing digital watermarking technology. To retrieve a watermark, extraction hardware and/or software need to be employed As the digital watermark usually have fairly large footprints, detectors employed to read the digital watermarks often require significant buffering storage. Consequently, this increases the detection costs, particularly if the watermark extraction is implemented in hardware.
In order to remedy this problem as well as other problems, alternative systems and methods need to be developed and employed to provide identification of images and/or documents to prevent counterfeiting.